We propose to characterize the autoimmune responses to neuronal cell surface and synaptic proteins that result in catatonia, autistic behaviors and other neuropsychiatric disturbances. In 2007, we reported a group of young women who acutely developed psychotic behavior or schizophrenia-like symptoms, subsequently followed by memory defects, catatonia, abnormal movements, and autonomic dysfunction. Using a set of techniques that we optimized, we found that all patients had antibodies against the NR1 subunit of the N- methyl-D-aspartate receptor (NMDAR), a glutamate receptor involved in synaptic transmission and plasticity. In about 60% of these patients, the trigger of the immune response was an ovarian teratoma that contained ectopic nervous tissue expressing NMDAR. Since that report, the number of patients with this disorder has rapidly increased, and similar clinical and laboratory strategies applied to patients with other neuropsychiatric disorders have resulted in the discovery of 6 novel immune responses to cell surface/synaptic autoantigens, including among others the GluR1/2 subunits of the AMPA receptor (AMPAR), the GABA(B1) receptor (GABA(B1)R), Leucine rich glioma inactivated 1 (LGI1) and Contactin associated protein 2 (Caspr2). This work is significant because: 1) the disorders affect young adults, including men and children with or without tumors; 2) they are responsive to immunotherapy; 3) some antibodies define new syndromes; 4) the characterization of the antigens has resulted in unambiguous diagnostic tests; and 5) patient antibodies have titer dependent and reversible effects on the function of the target receptors / proteins. Overall, these findings have led to the hypothesis that many subacute psychiatric disorders of unknown etiology, including catatonia or autistic behaviors, either alone or in association with other neurologic manifestations, are likely mediated by antibodies that affect neurotransmitter receptors at cell surface or synaptic sites. We will test this hypothesis in 3 goals. (1) We will select patients with one of 3 disorders for which we have preliminary evidence of serum or CSF antibodies to cell surface/synaptic proteins: rapidly progressive neuropsychiatric disorders with catatonic features, the spectrum of acquired rapidly progressive autistic behavior in children and adults, and limbic encephalopathy in children and adolescents. (2) We will identify the autoantigens in these 3 disorders, using highly sensitive methods we have developed and optimized to detect neuronal cell surface / synaptic antigens; and (3) We will use in vitro and in vivo studies to determine how patients' antibodies against novel cell surface/synaptic antigens affect neuron and synaptic structure and function, and how these recover after antibodies are removed. We will establish the autoimmune processes that lead to catatonia, autistic features, and limbic encephalopathy and the underlying cellular and synaptic mechanisms. Identification of autoimmune mechanisms will result in improved therapeutic interventions for these disorders in children and adults that will have a significant health impact and reduce the burden of neurological and neuropsychiatric disease.